Sainik School Entrance Exam 2018 Solved Paper

(b) A's 1 day work $=1/20$
B's 1 day work $=\frac{1}{12}$
B's 9 day work $=\frac{1}{12}\times 9=\frac{3}{4}$ part
Remaining work $=1-\frac{3}{4}=\frac{1}{4}$ part
$\because \frac{1}{20}$ part A can do in 1 day
$\therefore \frac{1}{4}$ part A can do in $20\times \frac{1}{4}=5$ days
So, A can finish the remaining work in 5 days.